1. Field of the Invention
The present invention relates to a photographic light-sensitve material and, more particularly, it relates to a photographic light-sensitive material in which formation of reticulation is prevented.
2. Description of the Prior Art
In order to increase the rate of producing photographic light-sensitive materials, the drying rate must be increased. To increase the drying rate, drying is conducted at an elevated temperature. However, the drying rate is limited since reticulation occurs at a temperature above a certain limit, generally 30.degree. C or more.
Also, exposed light-sensitive materials are processed at an elevated temperature to increase the rate of processings such as development, fixation, bleacing and washing. However, the processing temperature is also limited since reticulation occurs at a temperature above a certain limit.
In general, hardeners such as those described in C. E. K. Mees and T. H. James The Theory of the Photographic Process, 3rd. edition pp. 54-60, The Macmillan Co., New York, are added either to the photographic light-sensitive materials or to the processing solutions to prevent reticulation during processing. However, these methods have the defect that the addition of the hardener in a sufficient amount to prevent reticulation with conventional prior art materials often affects the photographic emulsion and retards the processing rate.
Therefore, a photographic light-sensitive material which is not subject to reticulation upon production and on processing thereof at an elevated temperature has been desired.
As one means to solve this problem, it is known to coat carboxymethylated casein or ethyl cellulose sulfate sodium salt on the uppermost layer of a photographic light-sensitive material. However, since carboxymethylated casein is prepared from a natural product, it has the devects that a product with uniform characteristics is difficult to obtain, that it possesses poor coating properties, and that it is difficult to remove impurities exerting detrimental influences on the photographic properties from this product. Also, with sodium salt of ethyl cellulose sulfate, it is difficult to obtain a water-solube product by converting ethyl cellulose to the sodium sulfate salt thereof. This is because the solubility properties obtained greatly depend upon the degree of ethylation and the degree of polymerization of the ethyl cellulose starting material. In order to obtain a sodium salt of ethyl cellulose sulfate product having a good solubility, the degree of ethylation and the degree of polymerization of ethyl cellulose is limited to an extremely narrow range. It is difficult to obtain such an ethyl cellulose with a good reproducibility. Ethyl cellulose is essentially poor in solubility. Therefore, when it is completely converted to the sodium sulfate salt, it becomes difficult to handle, i.e., it becomes insoluble in either water or organic solvents such as alcohol or acetone, which makes coating difficult. In addition, it is known that sulfuric acid esters in general have poor stability.
U.S. Pat. No. 3,835,582 Fowler, Jr., et al. discloses polymers (B) and (E) of the present invention. However, polymers (B) and (E) are always used in admixture with gelatin when the same are utilized as an uppermost non-light-sensitive layer in a photographic element. Fowler, Jr., et al. further do not disclose that the copolymers prevent reticulation. Typically, Fowler, Jr., et al. use a 1:1 gelatin-polymer coating solution (see, for examples, Col. 5, lines 25-28) whereas we, the inventors of the present application, have found that if a 1:4 gelatin-polymer coating solution is utilized reticulation cannot be prevented, as shown in Example 5 of the present application.
U.S. Pat. No. 3,655,407 McGraw discloses a copolymer utilized for thickening an aqueous composition of a hydrophilic colloid such as gelatin. The copolymer is present in the compositions disclosed in the McGraw patent in an amount of only 0.1 to 5% by weight of the hydrophilic colloid, however.
U.S. Pat. No. 3,512,985 Harvey discloses the utilization of a polymer as a binder for a photographic silver halide emulsion; the emulsion always contains a hydrophilic colloid, such as gelatin.
U.S. Pat. No. 2,391,181 Minsk et al discloses polymer (E) of the present invention. However, there are important differences between the invention described in the Minck et al. patent and the present invention. Firstly, the polymers used in Minsk et al must be soluble in an alkaline photographic developing solution so that development can take place in a conventional manner (see, Col. 1, lines 43-48). Secondarly, the polymers in the Minsk et al. patent are used only to protect an emulsion against the action of water and hypo in a negative during conventional contact printing. In the present invention, the uppermost layer is not soluble in alkaline developing solutions because it is used to protect the light-sensitive layer from the processing solution.
British Pat. No. 752,791 discloses the provision of a polymer layer on an emulsion layer containing a photographic image, i.e., the polymer layer is provided after emulsion has been processed. In such processing, the problem of reticulation does not occur.
U.S. Pat. No. 2,957,767 Williams discloses silver halide dispersions containing a polymer.
U.S. Pat. No. 3,608,465 Ching et al. discloses an emulsion layer covered by a film which imbibes processing solution; the film covers a photographic product after the film has been separated from the emulsion layer.
U.S. Pat. No. 3,218,298 Piganoil discloses a method for producing polymers.